B3 - Supernovae probing the Dark Energy

Project B3 investigates the physics and astrophysics of Type Ia
supernovae in order to check for systematic effects which might limit
their usefulness in constraining the cosmic expansion history H(z) out
to a redshift of about 2. In addition, guided by theory, the
high-quality data emerging from present and future supernova surveys
will be used to reconstruction H(z) without further model assumptions.

Type Ia supernovae, in their unprecedented capability as distance
indicators, are the only direct proof of the accelerated expansion of
the universe. The are now employed to probe the equation of state of
the dark energy throughout a large fraction of the history of the
universe. They are currently the only means to map the expansion
history of the universe out to a redshift of about 1 and to identify the
influence of the dominating energy density. The combination of
distances from the local universe to beyond a look-back time of half
the history of the universe gives potentially the best leverage on
dark energy and its changes, if any.

Several projects have been finished, are under way, or are planned to
observe SNe Ia at all redshifts, starting from very nearby ones to
search for systematic effects in their calibration, at intermediate
redshifts, and also very high redshifts, the aim being to determine
the equation of state parameter of dark energy and, possibly, also its
first derivative. In contrast, model independent ways of interpreting
the data have be developed recently. They require high data quality if
applied to constrain models of the dark energy. Guided by theoretical
modeling we will make an attempt create such a data set from existing
supernova data and from those to come. In addition, the
model-independent approach will also be applied to baryon acoustic
oscillation data as an independent way to get H(z).

Three-dimensional hydrodynamical simulation of a SNIa explosion. The first
image shows the density distribution 100s after the explosion. The second image
shows color-coded the distribution chemical composition of the same simulation.
Blue corresponds to unburned material, redder color intermediate mass elements
like magnesium, silicon and sulfur, the yellow region corresponds to material
rich in iron group elements.

With our refined numerical codes LEAFS (combustion hydrodynamics) and ARTIS (Monte-Carlo
radiative-transfer) we are in a position to perform 'parameter-free' numerical simulations of SNe Ia explosions and to predict the physical quantities which are needed for the investigation of systematic effects of metallicity, age and environment on their lightcurves and spectra, as well as different progenitor systems. In particular we investigate the question of whether the observed correlation between peak-luminosity and light-curve shape and other similar correlations can be understood in the framework of the explosion models and, thus, can be made more reliable and robust. Moreover, we will start a search of which parameters are crucial in determining the correlations.